1. Field of the Invention
This invention relates generally to optimizing the operation of high intensity discharge lamps and the like, and pertains more particularly to a method and circuit for optimizing such lamps in the growing of plants.
2. Description of the Prior Art
Although there are a number of special problems in controlling the artificial lighting utilized in the growing of plants within a growth chamber, some of the individual problems are also present in the control of high intensity discharge lamps and the like for more general illuminating purposes.
In U.S. Pat. No. 3,573,544, granted on Aug. 6, 1971 to Jerome Zonis et al on Apr. 6, 1971 for "Gas Discharge Lamp Circuit Employing A Transistorized Operator" some of the various problems that have been encountered in the past are succinctly set forth. As far as is known to me, these problems have not been effectively solved for commercial installations. The patent explains that a large number of circuits have been proposed for increasing the efficiency of operation of fluorescent lamps. The patent points out that a general approach has been to increase the operating frequency of the signal transmitted to the fluorescent tubes but that there are differences of opinion as to just what the optimum frequency is which will produce the most efficient operation.
It is of importance to appreciate that the above-identified patent stresses the failure of others to deal with the complex variable impedance of gas-filled tubes. In an effort to overcome this shortcoming, the patent being considered provides a well-matched resonant circuit for achieving maximum efficiency with a specific tube; however, the patentees recognize that, while the same circuit will operate other tubes of different size or power requirements, it will not do so as efficiently as for the tube for which it was specifically designed.
The above problem has been recognized in U.S. Pat. No. 3,648,106, issued on Mar. 7, 1972 to Joseph C. Engel et al for "Dynamic Reactorless High-Frequency Vapored Lamp Ballast." In this situation, the patentees explain that it has been discovered that for each particular type of discharge lamp there is a preferred optimum repetition rate of potential application which varies according to the impedance characteristic of the lamp. Therefore, the patentees vary the repetition rate so that the lamp being controlled can find its own preferred mode of operation. In addition to other shortcomings, the main one is that the frequency is not controlled in steps or increments so that both electronic resonance and acoustical resonance cannot occur.
In U.S. Pat. No. 3,710,177, issued on Jan. 9, 1973 to Richard Ward and titled "Fluorescent Lamp Circuit Driven Initially at Lower Voltage and Higher Frequency, " after ionization has occurred, the patentee recognizes that the frequency can be progressively reduced or done so in a step-wise fashion. The patent further explains that the switching can be controlled manually or by a sensing device. However, once the switching has been achieved, the lamp operation is continued without further step-wise control of the frequency. Thus, there is no optimization of the fluorescent lamp dealt with in this patent. While optimization can be important in controlling fluorescent lamps, it is extremely important in controlling high intensity discharge lamps, as will be considered in the paragraph below.
A bank of series-connected fluorescent lamps are energized by a power triode in U.S. Pat. No. 3,876,907, granted on Apr. 8, 1975 to Don F. Widmayer for "Plant Growth System." However, only relatively small current magnitudes are involved. Also, there is no attempt to control the amount of power to the fluorescent lamps by varying the current pulse width with a concomitant "hard" or fast fully on-fully off switching action. The system is relatively inefficient and would not be suitable for high intensity lamps in the 400-1000 watt range where relatively large current values are used.